The vehicular service equipment art includes a variety of means used for ascertaining and adjusting the alignment of vehicular wheels and for diagnosing and correcting other wheel related conditions. Such means can include instruments which often must be mounted in predetermined relation to some location on the wheel, particularly the rotational axis thereof. For instance, some wheel alignment systems include instruments such as sensors and positional indicators which must be precisely positioned in relation to the wheel axis for determining such parameters as the camber, caster and toe-in angles of the wheel. Some instruments can also require precise placement to enable communication via a wire or by optical or other means with instruments mounted on the other wheels or with a base unit.
The most common prior art devices for mounting alignment instrumentation operate by gripping an outer flange portion of the wheel rim at three or four radially spaced locations by forcing finger members radially outwardly or inwardly in a collective clamping action against the flange surface, such as disclosed in U.S. Pat. No. 4,167,817. The radial clamping action enables adjusting for different wheel diameters and operates to center the device on a wheel to enable an alignment instrument to be mounted in precise relation to the wheel axis.
Such prior art devices, however, are limited as the flange portion of the wheel rim must be exposed or at least accessible by the attachment device. This limitation has become important in light of several factors influencing modern automotive design. For instance, some fender designs cover or obscure a portion of the wheel rim, usually for styling or aerodynamic purposes, and can leave insufficient space between the fender and the wheel rim for the alignment instrument to be mounted. This problem becomes particularly acute when the wheel must be rotated with the attachment device mounted thereon. Another factor is the increasing use of wheels constructed of aluminum, magnesium, plastic coated steel and other materials, which wheels may not provide a suitable flange surface around the rim for gripping with the prior art devices. Such construction materials may also be relatively soft and can be objectionably marred by contact with the prior art devices. Still further, some proposed new tire constructions cover or envelope the wheel rim within the tire. Such constructions provide only rubber tire surfaces for gripping to which the prior art devices may not provide a sufficiently secure attachment. These design trends have led to a search for alternative locations for attachment to vehicular wheels for mounting alignment instrumentation and the like adjacent thereto.
The wheel lugs, which include a plurality of threaded members located in a circular pattern around the axis of the wheel, provide a desirable alternative location for attachment to a vehicular wheel. However, unlike the wheel rim which provides a uniform surface around the wheel to grip, the wheel lugs and their pattern of location can vary considerably from vehicle to vehicle and can include 4, 5, 6 or more lugs located in different diameter circular patterns. For instance, four and five lug patterns are commonly found on passenger cars. The threaded lug bolts or nuts can also have a variety of different sizes and shapes. Such variables, particularly the differences in geometry between the respective lug patterns, present a difficult challenge in the design of a single mounting apparatus which can be used with a wide range of wheels.
More particularly, on a wheel having a four lug pattern the lugs are evenly spaced at 90.degree. angular intervals around the wheel axis. Five lug patterns have lugs which are 72.degree. apart. Six and eight lug patterns have lugs which are 60.degree. and 45.degree. apart, respectively. Furthermore, even-numbered lug patterns, such as those including 4, 6, and 8, lugs, are symmetrical about two normal planes which intersect along the wheel axis. A five lug pattern, on the other hand, is symmetrical about only one plane. This is an important difference, as will be discussed below. A mounting apparatus for use with a variety of wheels must therefore be capable of attachment to all of these different lug patterns, and also various lug pattern diameters, while still enabling accurately locating an alignment instrument in desired relation to a wheel.